Multicatheter interstitial brachytherapy versus stereotactic radiotherapy with CyberKnife for accelerated partial breast irradiation: a comparative treatment planning study with respect to dosimetry of organs at risk

Abstract

Background The aim of the study was to dosimetrically compare multicatheter interstitial brachytherapy (MIBT) and stereotactic radiotherapy with CyberKnife (CK) for accelerated partial breast irradiation (APBI) especially concerning the dose of organs at risk (OAR-s). Patients and methods Treatment plans of thirty-two MIBT and CK patients were compared. The OAR-s included ipsilateral non-target and contralateral breast, ipsilateral and contralateral lung, skin, ribs, and heart for left-sided cases. The fractionation was identical (4 x 6.25 Gy) in both treatment groups. The relative volumes (e.g. V100, V90) receiving a given relative dose (100%, 90%), and the relative doses (e.g. D0.1cm3, D1cm3) delivered to the most exposed small volumes (0.1 cm3, 1 cm3) were calculated from dose-volume histograms. All dose values were related to the prescribed dose (25 Gy). Results Regarding non-target breast CK performed slightly better than MIBT (V100: 0.7% vs. 1.6%, V50: 10.5% vs. 12.9%). The mean dose of the ipsilateral lung was the same for both techniques (4.9%), but doses irradiated to volume of 1 cm3 were lower with MIBT (36.1% vs. 45.4%). Protection of skin and rib was better with MIBT. There were no significant differences between the dose-volume parameters of the heart, but with MIBT, slightly larger volumes were irradiated by 5% dose (V5: 29.9% vs. 21.2%). Contralateral breast and lung received a somewhat higher dose with MIBT (D1cm3: 2.6% vs. 1.8% and 3.6% vs. 2.5%). Conclusions The target volume can be properly irradiated by both techniques with similar dose distributions and high dose conformity. Regarding the dose to the non-target breast, heart, and contralateral organs the CK was superior, but the nearby organs (skin, ribs, ipsilateral lung) received less dose with MIBT. The observed dosimetric differences were small but significant in a few parameters at the examined patient number. More studies are needed to explore whether these dosimetric findings have clinical significance.

The value of brachytherapy in the age of advanced external beam radiotherapy: a review of the literature in terms of dosimetry

“…However, the doses to OARs close to the target volume can be kept low due to the large effect of the inverse square law. This claim is supported by the results of some studies showing that skin, ribs and small ipsilateral lung volumes exposed to high doses are better protected by BT than by EBRT [ 20 , 22 , 23 ].

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“…In the more conformal CK plans, the doses to skin, ipsilateral lung and ribs were higher compared to BT: skin D 1cm3 was 86.1% vs. 46.1% ( p = 0.0018), ipsilateral lung D 1cm3 45.0% vs. 38.4% ( p = 0.0272) and ribs D 1cm3 73.6% vs. 49.0% ( p = 0.0013), but the heart was slightly better protected with CK (D 1cm3 10.5% vs. 11.2%, p = 0.0534). Then, in another study, MIBT and CK were dosimetrically compared using two separate patient cohorts [ 23 ]: 32 APBI patients received their treatments with MIBT and another 32 with CK. The protocol for target volume definition and the fractionation were identical in the two groups.…”

“…Doses to contralateral breast and lung were small with both techniques, but CK resulted in smaller values. We note that in both studies [ 22 , 23 ], CK treatments were performed with tracking and an MLC-based step-and-shoot IMRT technique, and an isotropic margin of 2 mm around the CTV was used to create the PTV.…”

“…Analysis of the pooled data from the three studies [ 20 , 22 , 23 ] shows that the mean V50 values for the non-target breast are 10.0% vs. 15.3%, D 1cm3 values for the ipsilateral lung are 37.8% vs. 48.2%, D 1cm3 values for the skin are 54.9% vs. 84.3%, and D 1cm3 values for the ribs are 45.9% vs. 70.6% in favour of BT.…”

“…Boost doses following whole-breast irradiation can also be effectively delivered with BT [19,75]. Charagvandi et al [18] have dosimetrically compared single-fraction ablative RT with interstitial BT and VMAT K [17] 3D-CRT, HT 13 BT 10, 5, 0 Margin: 3D-CRT 10 mm, supine HT 5 mm, prone HT 0 mm Charagvandi [18] VMAT 20 VMAT NR Single-fraction ablative radiotherapy Terheyden [19] 3D-CRT 136 Two patient cohorts NR Boost was given to 36 patients with BT and to 100 with 3D-CRT Major [20] IMRT 34 BT 5 4-5 coplanar beams for IMRT Shahbazian [21] 3D-CRT 15 BT 5 Deeply seated tumours Fröhlich [22] SBRT with CK 25 CK 2 Virtual BT plans on CTs with contours for CK Herein [23] SBRT with CK 32 Two patient cohorts 2 Comparison between real treatment plans Periasamy [24] VMAT 50 Two patient cohorts 5 Tumour bed boost after whole-breast irradiation Gynaecological Georg [25] IMRT, IMPT 9 BT 3-5 High-tech EBRT vs. high-tech BT Shwetha [26] IMRT 10 BT NR Pear-shaped dose distribution of BT mimicked by IMRT Gielda [27] HT 6 BT 0 3-5 mm CTV-PTV margin for BT and HT Sharma [28] IMRT 12 BT 3-5 Interstitial BT vs. IMRT for cervical cancer Cengiz [29] SBRT with CK 11 BT 0 BT with a tandem and two ovoids with dosimetry on point A Neumann [30] CK 11 CK + real BT patients 0 Emulating BT-like inhomogeneous dose distributions Khosla [31] IMRT 15 BT and IMRT 10 Two series of CT scans, one for BT and one for IMRT Otahal [32] CK 10 BT 0 MRI-based intracavitary and interstitial BT Pinzi [33] IMRT 15 BT 7-10 BT and IMRT for boost only Wali [34] VMAT 10 BT 5 Boost with VMAT in replacing BT Jones [35] SBRT with HT 15 BT 2 Endometrium, 2 mm CTV-PTV margin in HT plans Kauffmann [36] 3D-Arc and SBRT [20]. For 34 patients with early-stage breast cancer treated with interstitial HDR-BT, additional IMRT plans were created using identical CT data and contours.…”